1. Field of the Invention
The present invention relates to a multiwavelength light source for emitting light having multiple wavelengths.
2. Description of the Related Art
In a recent optical communication system, increasing a communication capacity has been tried by applying high-density wavelength division multiplexing. High-density wavelength division multiplexing optical communication requires a multiwavelength light source for emitting light having multiple wavelengths spaced a distance as very short as 1 nm or less, and accordingly a very high spectral accuracy is required. At present, size reduction of a light source for wavelength division multiplexing optical communication is required. The present invention is a technique for realizing oscillation at wavelengths with an accurate spacing in a laser diode array module to thereby realize a small-sized multiwavelength light source.
Conventionally, a multiwavelength light source is realized generally by using multiple light sources having different oscillation wavelengths. However, with this configuration using such multiple light sources, a very large installation space is necessary, and temperature control of the multiple light sources must be individually performed, causing a great increase in scale of the multiwavelength light source. As another multiwavelength light source recently researched, the refractive index and period of each grating of a DFB (distributed feedback) laser diode array or DBR (distributed Bragg reflector) laser diode array are changed to oscillate laser diodes constituting the array at different wavelengths.
Further, a multiwavelength surface-emitting laser array formed by integrating lasers oscillating at different wavelengths is disclosed in U.S. Pat. No. 5,029,176. The oscillation wavelength of a surface-emitting laser is determined by the resonant wavelength of a vertical cavity, and the resonant wavelength is determined by a cavity length. Accordingly, by inclining the thickness of each layer constituting the surface-emitting laser in an in-plane direction, it is possible to simultaneously form lasers having different oscillation wavelengths.
Although the multiwavelength light source obtained by changing the refractive index and period of each grating of the DFB laser diode array or DBR laser diode array has a small size, the wavelength spacing in the array is affected by a refractive index distribution during manufacture, thus presenting a problem in manufacturability. Further, the multiwavelength surface-emitting laser array disclosed in U.S. Pat. No. 5,029,176 also has a problem in manufacturability because the surface-emitting laser itself is difficult to manufacture.